GLAST Large Area Telescope: Grid interface proposal Alessandro Brez INFN Pisa

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Grid interface proposal Alessandro Brez INFN Pisa

2. Ti ¼”+1mil Al ¼” 4.95mm thread Steel screw with shoulder ¼”-3mils Last failure • The last vibe test failed essentially because: • The tolerance between screw shoulder and grid hole was too large (~0.1mm) • The screwed part was too short (~3mm) • The steel shoulder damaged the Al hole • Result: the 4 corner screws were unlocked

3. Proposal • The tolerance between screw shoulder and flexure/grid hole has to be tight on long • The grid has to be reinforced with an insert that distributes the load on a larger diameter. • We consider the idea to have the tight tolerance by construction even on few points (3) dangerous, we can have real problems mounting all the towers (3X16 joints). The possibility to have a failure mounting one tower cannot be excluded. • In the EM tower, with a simplified coupling (cylindrical holes ¼”) we could mount the tower to the grid because there was a 0.1mm tolerance in the shoulder-hole coupling

4. Our concept To guarantee a safe and symmetric joint we propose to separate the alignment points from the joint points. 1) Mount the alignment jig to the bottom tray 2) Dry test 3) Put the inserts with epoxy 4) Align back the tower to the grid 5) Place the screws, RT cure of the adhesive 6) Final torque of the screws, alignment tool is removed

5. Alignment tool Reference points 3 (the same reference points used for sidewall mounting) The alignment tool is mounted on the bottom tray using the bottom tray reference holes and the M2.5 threaded holes

6. Reference to the grid On the grid there are 3 other reference holes. The pin/hole tolerance can be 20mm without mounting problems (3 points)

7. Inserts

9. The inserts